The main types of vehicle dynamics control systems are anti-lock brake and traction control systems (ABS/TCS). Control systems of this type are used to influence the longitudinal dynamics of the vehicle. These concepts also include control systems for motor vehicles that are used to influence the vehicle's transverse dynamics. These, for example, include control systems for controlling a quantity describing the vehicle yaw rate (VSC/ESP system). A system of this type can, among other things, influence the steering performance of motor vehicles (for example, taking into account the yaw rate, steering angle, float angle, etc.).
A brake system that includes means for performing anti-lock braking and traction control functions is described in the article entitled "Antiblockiersystem und Antriebsschlupfregelung der 5. Generation" (Fifth-Generation Anti-lock Brake and Traction Control System), by Wolf-Dieter Jonner, Wolfgang Maisch, Robert Mergenthaler, and Alfred Sigl, published in ATZ Autmobiltechnische Zeitschrift 95, 1993, Vol. 11. The hydraulic valves and the pump elements used to build up and relieve pressure are combined into a hydraulic unit. Particularly in the case of traction control, it is desirable to know the temperature of the brake system (the hydraulic unit and thus the hydraulic system), in particular the temperature of the coils of the respective solenoid valves. Measures for taking into account the brake system temperature are not described for the conventional brake system.
Hydraulic units used in the vehicle stability control systems listed above (ABS, TCS, ESP, VSC) provide valves that can operate in either a linear or proportional fashion. The linearly settable pressure drop across the valve according to a characteristic function depends on the valve current. However, the valve coil resistance is greatly dependent on coil temperature. Therefore, the valve current and pressure drop when setting a specific valve voltage are also greatly dependent on temperature. To avoid inaccuracies that this can produce in vehicle stability control, a conventional method measures the temperatures at the respective coils and takes into account a corresponding correction factor on the basis of the measured temperatures in controlling the coils. However, it has proven to be extremely cumbersome to measure the temperature at all valve coils.
To obtain reliable measurement results, it is especially important to use, for example, valves with current-controlled valve output stages. However, such valve output stages, and the valves equipped with them, are relatively expensive.
Corrective measures to compensate for temperature influences are conventional, for example, for solenoid valves used to control the metering of fuel in an internal combustion engine. Thus, an internal combustion engine in which the time of activation of the solenoid valve can be corrected as a function of solenoid valve temperature is described from German Patent Application No. 196 06965.